NEW YORK (Reuters Health) - Sleep-disordered breathing (SDB) in pre-school children does not affect their nocturnal blood pressure dipping, as it generally does in adults, new research from Australia suggests.

"In healthy people, blood pressure falls during sleep, providing a period of rest for the cardiovascular system. In adults with obstructive sleep apnea (OSA), this fall in blood pressure ("dipping") is lost. Our study showed that dipping of blood pressure during sleep is preserved in young children with obstructive sleep apnea," said co-senior author Dr. Rosemary S. C. Horne in an email to Reuters Health.

At Monash University in Melbourne, Victoria, Australia, her group found that preschool children with SDB showed a significant rise in pulse transit time (PTT) from wake to sleep, which suggests a fall in BP and a nighttime reduction in heart rate (HR).

"This is important, as it means that these young children do not yet have all the cardiovascular consequences that are associated with this condition in adults. Diagnosing and treating the condition early may prevent development of more persistently elevated blood pressure," Dr. Horne said.

Dr. Horne believes doctors should screen young children for sleep-disordered breathing, so the children can be treated before problems arise.

"Sleep-disordered breathing has significant effects not only on the cardiovascular system but also on daytime behavior and school performance. These effects are milder in preschool children compared with school-aged children and are improved with treatment," she said.

"OSA in otherwise healthy children is usually due to enlargement of the tonsils and adenoids. If a child has large tonsils and/or persistent nasal obstruction, then a focused history for symptoms of OSA should be taken," said co-senior author Dr. Lisa M. Walter in an email.

What should parents watch for? Co-author Dr. Gillian M Nixon said in an email that snoring is a common symptom in children - often overlooked by parents and doctors - that can be a sign of obstructive sleep apnea.

"Snoring and sleep apnea can lead to poor quality sleep. If parents are concerned about the way their child breathes when asleep, especially if the child seems to be struggling to breathe or is excessively restless during sleep, then referral to a sleep specialist or ENT surgeon may be warranted," she said.

The authors think theirs is the first study to evaluate nocturnal dipping of BP as suggested by an increase in PTT and HR in preschool-aged children with SDB.

They recruited 192 children, ages three to five. As reported online February 12 in Sleep Medicine, 163 were available for the nocturnal dipping analysis: 66 with primary snoring (PS), 34 with mild OSA, 28 with moderate-to-severe (MS) OSA, and 35 controls who did not snore and had no more than one event of hypopnea per hour.

Of the 179 children who took part in the sleep fragmentation study, 72 had PS, 31 had mild OSA, 38 had moderate-to-severe OSA, and 38 were controls.

The groups were similar in age, gender, wake BP z-scores and traditionally-measured sleep efficiency, but the BMI z-score was significantly higher in the mild OSA group than in the other groups (p<0.05 for all).

The researchers gave all the children routine overnight polysomnography and recorded their pulse transit time (PTT) and heart rate (HR) during total sleep time as well as their first period of non-rapid-eye-movement REM stages 1 and 2 (NREM1/2), NREM3/4 and REM sleep, and they calculated the number of sleep stage transitions or awakenings per hour of sleep (the sleep fragmentation index, SFI).

The OSA severity measurements were significantly higher in the MS OSA group compared with the other groups (p < or = 0.01 for all).

They found no significant group difference in percentage change in PTT or HR from wake to sleep in any sleep periods they analyzed and no significant group differences in absolute HR during wake or any sleep periods they analyzed. The moderate-to-severe SDB group had a higher SFI than the PS or the mild SDB groups (p<0.05 for both) and the controls (p=0.07).

Sleep stage had a significant effect on percentage change in PTT and HR from wake (p<0.001 for both); PTT rose an average of 8% and HR fell by 14% from wake to total sleep.

The change to total sleep was significantly greater than to specific sleep stages (p<0.05 for all) and was significantly less to NREM1/2 than to all other stages (p<0.001 for all). The percentage change in HR from wake to NREM3/4 was greater than to REM sleep (p<0.001), but the percentage change in PTT was similar from wake to NREM3/4 and to REM sleep. The absolute HR differed significantly in all wake and sleep periods analyzed (p<0.001 for all).

"The increase in blood pressure seen even in very young children is an important reason to screen for the condition. Although our study showed preservation of nocturnal dipping in pre-school children, we have also demonstrated increased blood pressure in REM sleep in children in this age group with moderate to severe OSA," said Dr. Nixon in an email.